Battleblog #7 has details on the themed co-op campaign DICE is working on for Battlefield 3, their upcoming military shooter sequel. Here's a bit on how this works:

To survive through the co-op missions, you’ll need to stay close to your buddy. If he goes down, lend a helping hand with the new co-op “Man down!” mechanic, that lets you revive him in the heat of battle. While being down, you can still use your secondary weapon to defend yourself, while slowly crawling to a safer spot where your friend can help you without getting shot. If both of you go down, it’s game over.

You fight together. You die together. And you score together. After having cleared a co-op mission with your friend, your total combined score will be displayed via Battlelog, our suite of free social features that connect all Battlefield 3 players. Missions are designed to be shorter than single player missions, so you can easily do multiple rounds in an evening to try and beat your friends’ high score. The best score of your Friend will be displayed for each mission, so you know what to aim for.